Field of the Invention
The present disclosure relates to the field of air compressors adapted for supplying compressed air to pneumatic units and, in particular, to a valve stem for an integral high pressure cylinder unloader valve used on a railway vehicle air compressor.
Description of Related Art
The use of a multiple stage, multiple cylinder air compressor is well known in the art. It is common practice to use a multiple stage, multiple cylinder air compressor on a locomotive or other railway vehicle to provide compressed air that is consumed by various pneumatic devices throughout the locomotive and railcars to provide a variety of functions. The primary function is to operate the locomotive and railcar brakes. Several air compressors currently used in the railway industry are designed with an unloader system which, when activated with pilot air pressure, will, under normal operation, release the air pressure contained or “bottled” in the volume between a high pressure compressor head and a high pressure piston. The pilot air pressure is typically delivered from a locomotive compressor magnet valve (CMV), which is not provided as a part of the compressor assembly. The CMV provides pilot air pressure to a compressor unloader system to change the air compressor's state to an unloaded state (not pressurizing air) and does not provide pilot air pressure to the compressor unloader system to change the air compressor's state to a loaded state (pressurizing air). Pilot air pressure must be maintained to keep the air compressor in an unloaded state. In certain scenarios, during improper locomotive operation, power is cut to the CMV with the air compressor in an unloaded state. In these undesirable scenarios, downstream air pressure may be fed back into the volume contained between the high pressure cylinder head and the high pressure piston. When the locomotive is placed back into proper operation and the CMV once again sends pilot air to the compressor unloader system, the air pressure now contained within the volume prevents the compressor unloader system from properly actuating. In this scenario, the compressor unloader system will not dissipate the air pressure contained in the volume.
Many locomotive air compressors are equipped with motors rated with just enough horsepower for normal operation and startup, where the air compressor will not be pressurized in the volumes contained between the low pressure heads and the low pressure pistons, and in the volumes contained between the high pressure heads and the high pressure pistons. Since the motors are not adequately sized to start an air compressor when an initial air pressure is already contained in these volumes, many motors will stall when attempting to start in this undesired scenario caused by improper locomotive setup.
Therefore, there is a current need for an air compressor with an integral high pressure cylinder unloader valve that allows the air pressure trapped in the volumes to be exhausted to atmosphere. There is also a current need for a quick and efficient method of machining an air compressor head to provide a means for dissipating the air pressure contained in the volumes. There is also a current need for a valve stem that provides fluid communication between the volumes and atmosphere to effectively dissipate the air pressure from the volumes.